Author Topic: eev blog 262  (Read 34413 times)

0 Members and 1 Guest are viewing this topic.

Offline bpkdasbaum

  • Newbie
  • Posts: 3
Re: eev blog 262
« Reply #50 on: April 09, 2012, 11:14:56 pm »
@amspire @ Dave.S

Okay, I copied both circuits now and added my fans  :P (hopefully I copied yours correctly amspire)

I did read up on inductive spiking too: As far as I understood a diode parallel to the fans will do the trick (and circle the overload back into the fans until it dissipates). Question is do I really need to care about this in either of the circuits, since the fans are quite small (15x15x3 milimeter, specs in image below)?


So, will either of the circuits work? If not, why and what needs to be changed?

Edit:

Oopps forgot circuits:





« Last Edit: April 09, 2012, 11:19:44 pm by bpkdasbaum »
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 29911
  • Country: au
    • EEVblog
Re: eev blog 262
« Reply #51 on: April 10, 2012, 05:46:15 am »
To me the method in general is not a robust solution as it depends a so much on the way the load behaves. For example, a transient from the load circuit can turn the supply on, even if the switch is not touched. If your load was a linear regulator IC with a reverse diode across it, and you attach an external load to the regulator output which happens to have a charged supply cap, then this switch circuit will turn itself on

That right there is what you call a feature  ;D

Dave.
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 29911
  • Country: au
    • EEVblog
Re: eev blog 262
« Reply #52 on: April 10, 2012, 05:48:19 am »
Dave, you are using the wrong color marker on the whiteboard.  Please stop it.  ;)  :P

No, your monitor is just out of whack. Twiddle the colour knob until correct  :P

Dave.
 

Offline Ben

  • Newbie
  • Posts: 1
Re: eev blog 262
« Reply #53 on: April 17, 2012, 11:47:26 pm »
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: eev blog 262
« Reply #54 on: April 23, 2012, 07:44:48 am »
Hello Every body,

I didn't see no comments on the fact that there could be RF present on the input and output
of this switch hi...

But I maybe should add a diode in series with the capacitor so the voltage will drop
to zero also if the is almost or no load.

There are many TFT TVs that switches on and off if I transmit close to it with my 2/0.70 5 Watt  handheld.

Very annoying hi...

I think that this issue needs to be addressed. Is this circuit RF interference resistant to a reasonable degree?
 

Offline timelessbeing

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: 00
Re: eev blog 262
« Reply #55 on: May 07, 2012, 05:41:47 am »
Great video. I just happened to need a soft switching circuit similar to this, only I'm a 'noob' and I don't have 'mad skillz' yet.

I have a 12V source, three loads (LEDs), and a common return. I want to use a momentary micro switch to toggle between four states:
1. off
2. turn on load 1
3. turn on load 1 + 2
4. turn on load 1 + 2 +3

I have seen this type of behaviour in LED headlamps. Is it possible to create using common components like Daves?

Tap on Dave! 8)
« Last Edit: May 07, 2012, 06:05:28 am by timelessbeing »
 

Offline Scarionn

  • Contributor
  • Posts: 18
Re: eev blog 262
« Reply #56 on: June 10, 2012, 02:42:30 am »
Hi dave. Really good design but, how I do a normally ON latch switch? Like a multimeter.
Having just one pole rotary switch.
 

Offline natezimmer

  • Newbie
  • Posts: 1
Re: eev blog 262
« Reply #57 on: August 18, 2012, 12:59:54 pm »
Issue I see with this circuit is that if your input is say 20V, you stand a decent chance of damaging the pmosfet due to exceeding VGS max. Anyone know a simple way around that while still using the pmos switch? (lowering the supply voltage doesn't count  ;) )
 

Offline pbendel

  • Contributor
  • Posts: 10
Re: eev blog 262
« Reply #58 on: December 08, 2012, 11:59:27 pm »
Does anybody have one that works with smd components?
  I am not that lucky I guess...
 
 

Offline electroguy

  • Regular Contributor
  • *
  • Posts: 78
  • Country: au
Re: eev blog 262
« Reply #59 on: December 09, 2012, 01:08:28 am »
Issue I see with this circuit is that if your input is say 20V, you stand a decent chance of damaging the pmosfet due to exceeding VGS max. Anyone know a simple way around that while still using the pmos switch? (lowering the supply voltage doesn't count  ;) )

5V to 10V Zener across the gate-source might work?
I use a Zener across G-S when using a pfet for reverse polarity protection, works a treat up to VDS (usually 60V and above) while making sure VGS is still under 20V
There are 10 types of people that understand binary, those that do and those that don't!
 

Offline onlooker

  • Frequent Contributor
  • **
  • Posts: 385
Re: eev blog 262
« Reply #60 on: December 11, 2012, 02:54:17 am »
This would be my solution if switch-on-ground and load-independent are required. This is actually a simplified and extended version of one I used for UT61E mod. In that sense, it works as a real circuit.

It works like this:short press of switch (<0.5s) does turn-on; long press of switch (>0.5s) does turn-off. The time constant can be changed by changing C1.

For resistive loads, M3Vto-2 is not needed and loads should be parallel to R4. M3Vto-2 is purely for separating power supply path from switch ctrl path.



 

Offline Jeremyvnc

  • Contributor
  • Posts: 7
  • Country: us
Re: eev blog 262
« Reply #61 on: January 11, 2013, 03:27:56 am »
This is driving me bonkers!  I have been able to breadboard two different designs but when I go to make the pcb with smd components, it no longer works.

Can you all please tell me what I'm doing wrong?

Attached is my schematic.

The 5uF capacitor is actually a 4.7uF tant cap.
The diode is a STPS1L30A Schottky diode.
The P-channel is a IRLML2246TRPBF
the N-Channel is a IRFML8244TRPBF

What I'm seeing is the controlled device either just stays on or it will drop the voltage for a moment enough to reset.
When I breadboarded it, the circuit would start in the off state, push the button and it turns on, wait a few seconds and press it again to turn it off.  Exactly what I need.

Pleeease help me...  |O
-Jeremy
 

Offline Ebis

  • Newbie
  • Posts: 2
  • Country: scotland
Re: eev blog 262
« Reply #62 on: October 09, 2015, 01:22:11 pm »
Hi everyone

A bit of a necro but maybe someone will point me in the right direction.

I was trying to base an on/off touch button on one of these designs, getting the touch functionality proved fairly easy with swapping out the tactile for an NPN, tying the base to a touchable pad, throwing in some small capacitors to adjust sensitivity. This worked fine on a breadboard with no real load attached.

But
When I attach my  load (a string of parallel&serial bound LEDs with a bit of resistance in front) I get a huge voltage drop across the pMOSFET. So i returned to the initial designs, removed all my additions and ported to falstad to investigate.
What I found is the designs all works great with a load of a 100 Ohms or so, but my load  should be pulling between 500-700mA.
As an added bonus I'm trying to power it off an old phone charger which when just loaded with the LEDs and some minor resistance (11Ohm) in series is happy to spit out 700mA at 7.7V which is ok for the load but exceeds the values my transistors are happy to take.. (the charger is rated at 1A so all good there)

If anyone has any insight or suggestions they are willing to share it would be much appreciated.
Though I always dabbled in tech, but I only started studying electronics in detail fairly recently and it feels like the answer is a year of books away...
 

Offline Ebis

  • Newbie
  • Posts: 2
  • Country: scotland
Re: eev blog 262
« Reply #63 on: October 12, 2015, 01:07:43 pm »
Here is my take on the on/off latching button, only ran it in falstad so far, need to try breadboarding it.
There are probably several issues with it, I will be most grateful if anyone points them out, or maybe explains the math behind it so a better version can be made. This one is a little bit sensitive to how long you need to hold the tactile.

Also... the simulator is showing double the expected voltage on the capacitor when circuit is in on state, is that just a simulator artefact?


http://tinyurl.com/p2ysh4s


p.s: 4 components - do I win?
« Last Edit: October 12, 2015, 01:14:00 pm by Ebis »
 

Offline 4JimBeam

  • Contributor
  • Posts: 5
  • Country: de
Re: eev blog 262
« Reply #64 on: February 18, 2016, 03:46:07 pm »
@Ebis:

I tried your ciruit with LT Spice, it does waste a lot power in the N-Mos and did not switch off.  ???

Did you / anyone tried this ciruit in real?

 

Offline timelessbeing

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: 00
Re: eev blog 262
« Reply #65 on: February 19, 2016, 05:36:08 am »
I built the one in this patent:
http://www.faqs.org/patents/imgfull/20090237065_01

It works fine. I did not test it with any heavy duty loads, though.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf